1. Field of the Invention
The present invention relates to a wireless system, and more particularly, to a method of random access in a wireless communication system.
2. Discussion of the Related Art
First of all, a random access method in a wireless communication system according to a related art is explained with reference to FIG. 1 as follows. FIG. 1 is a diagram for a random aces method in wireless communication system according to a related art.
Referring to FIG. 1, a mobile station selects one of ranging codes from a bandwidth request code (BR code) set to request an uplink bandwidth and then transmits the selected one to a base station [S110]. The mobile station starts a timer after having transmitted the bandwidth request code to the base station. In this case, the timer is a contention-based reservation timeout or a T3.
Having normally received the code transmitted by the mobile station, the base station allocates an uplink resource for sending a bandwidth request (BW-REQ) message to the mobile station [S120]. If the mobile station fails to have the uplink resource allocated thereto until the timer ends after transmission of the bandwidth code, it retransmits the bandwidth code.
The mobile station sends a bandwidth request message via the allocated region [S130]. Having received the bandwidth request message transmitted from the mobile station, the base station allocates an uplink resource to the mobile station [S140]. Subsequently, the mobile station transmits data to the base station via the allocated uplink resource [S150].
In the following description, a random aces method in a future broadband wireless access system is explained with reference to FIG. 2. FIG. 2 is a diagram for a random access method in a future broadband wireless access system.
First of all, in a future broadband wireless access system, a base station simultaneously supports a general 5-step scheme and a 3-step scheme (quick access scheme) both. The 5-step scheme is usable in a manner of being independent from the 3-step scheme or can be used in a 3-step fallback mode.
According to the 3-step scheme, referring to FIG. 2, a mobile station sends a quick access message including a bandwidth request indicator selected randomly or by a predetermined rule and uplink bandwidth request information to a base station [S210]. In this case, the bandwidth request indicator can be a bandwidth request (BR) sequence or a bandwidth request code. And, the uplink bandwidth request information can include a mobile station ID (station ID), a bandwidth request size and the like.
The base station transmits ACK/NACK (acknowledgement/negative acknowledgement) in response to the bandwidth request indicator to the mobile station [S220]. Having normally received the bandwidth request indicator and the quick access message, the base station allocates an uplink resource for data transmission to the mobile station [S260]. The mobile station then transmits data to the base station via the allocated resource [S270]. In doing so, the mobile station is able to transmit additional uplink bandwidth request information to the base station.
According to the 5-step scheme, if a mobile station transmits a randomly selected bandwidth request indicator to a base station [S210], the base station transmits ACK/NACK to the mobile station in response to the bandwidth request indicator from the mobile station [S220]. The base station allocates an uplink resource for a bandwidth request message transmission to the mobile station via CDMA Allocation A-MAP IE (advanced MAP information element) [S230].
The mobile station sends a bandwidth request message to the base station via the allocated region [S240]. If so, the base station transmits ACK/NACK to the mobile station in response to the bandwidth request message [S250]. The base station allocates an uplink resource to the mobile station via an uplink basic assignment A-MAP IE (UL basic assignment A-MAP IE) [S260]. The mobile station then transmits data to the base station via the allocated region [S270]. In doing so, the mobile station is able to transmit additional uplink bandwidth request information to the base station.
FIG. 3 is a diagram of a ranging process in a wireless communication system according to a related art.
Referring to FIG. 3, in order to perform initial ranging, a mobile station selects one of ranging codes from an initial ranging code set and then transmits the selected ranging code to a base station [S310]. Having normally received the ranging code from the mobile station, the base station allocates an uplink resource for transmitting a ranging request message (Ranging-REQ message) to the mobile station [S320]. According to a temporal status of the ranging code, the base station is able to send a ranging response message (Ranging-RSP message) to the mobile station. If the mobile station fails to receive the uplink resource or the ranging response message until the end of a timer (a content-based reservation timeout or T3), which started after transmission of the ranging code, the mobile station retransmits the ranging code.
The mobile station, to which the uplink resource for sending a ranging request message has bee allocated, sends the ranging request message via the allocated region [S330]. If so, the base station sends a ranging response message to the mobile station [S340]. In this case, the ranging includes handover ranging and periodic ranging as well as the initial ranging.
In the following description, explained are a process for requesting an uplink bandwidth by random access in a future broadband wireless access system and a process for performing a ranging in a future broadband wireless access system.
FIG. 4 is a diagram of a process for requesting an uplink bandwidth in a future broadband wireless access system.
First of all, in a future broadband wireless access system, a base station simultaneously supports a bandwidth request process of a general 5-step scheme and a bandwidth request process of a 3-step scheme (quick access scheme) both. The 5-step scheme is usable in a manner of being independent from the 3-step scheme or can be used in a 3-step fallback mode.
According to the 3-step scheme, referring to FIG. 4, a mobile station sends a quick access message including a bandwidth request indicator selected randomly or by a predetermined rule and uplink bandwidth request information to a base station [S410]. In this case, the bandwidth request indicator can be a bandwidth request (BR) sequence or a bandwidth request code. And, the uplink bandwidth request information can include a mobile station ID (station ID), a bandwidth request size and the like.
The base station transmits ACK/NACK (acknowledgement/negative acknowledgement) in response to the bandwidth request indicator to the mobile station [S420]. Having normally received the bandwidth request indicator and the quick access message, the base station allocates an uplink resource for data transmission to the mobile station [S460]. The mobile station then transmits data to the base station via the allocated resource [S470]. In doing so, the mobile station is able to transmit additional uplink bandwidth request information to the base station.
According to the 5-step scheme, if a mobile station transmits a randomly selected bandwidth request indicator to a base station [S410], the base station transmits ACK/NACK to the mobile station in response to the bandwidth request indicator from the mobile station [S420]. The base station allocates an uplink resource for a bandwidth request message transmission to the mobile station via CDMA Allocation A-MAP IE (advanced MAP information element) [S430].
The mobile station sends a bandwidth request message to the base station via the allocated region [S440]. If so, the base station then allocates an uplink resource to the mobile station via an uplink basic assignment A-MAP IE (UL basic assignment A-MAP IE) [S460]. The mobile station then transmits data to the base station via the allocated region [S470]. In doing so, the mobile station is able to transmit additional uplink bandwidth request information to the base station.
FIG. 5 is a diagram of a process for performing a ranging in a future broadband wireless access system.
Referring to FIG. 5, if a mobile station transmits a ranging indicator to a base station [S510], the base station transmits ACK/NACK to the mobile station in response to the ranging indicator [S520] and allocates an uplink resource for a ranging request message transmission to the mobile station [S530]. If so, the mobile station sends a ranging request message to the base station [S540]. The base station then sends a ranging response message to the mobile station [S550].
As mentioned in the above description, in a broadband wireless access system, a base station receives such a random access code as a bandwidth request indicator and a ranging indicator from a mobile station and then transmits a corresponding ACK/NACK to the mobile station. Therefore, a method of minimizing an overhead of the ACK/NACK is necessary.